Extent Of Post-juvenile Moult Research Articles

Plumage dimorphism and moult patterns of weaverbirds – a review

The colourful plumages of weaverbirds (family Ploceidae, with 118 species recognised) provide a well-known and in part iconic showcase of sexual selection, with widespread sexual dimorphism (93 species) as well as seasonal dimorphism (62 species). The tremendous diversity in both the type and degree of plumage dimorphism is poorly known, which calls for a better and extended understanding of the highly variable moult patterns in this group. Here, we lay a foundation for this by reviewing and discussing what is known of the timings and patterns of moult in the Ploceidae. The extent of post-juvenile moult is poorly known in weavers: it is known to be complete in 10 species, partial in two species, and either complete or partial in six species. However, it is likely that there is more variation than previously thought. Weavers typically have a complete moult after breeding, and before breeding a partial prenuptial moult, restoring the male (and, in some species, female) breeding plumage; this usually involves only body feathering, one exception being the Seychelles Fody Foudia sechellarum, which has a complete prenuptial moult. We compiled primary moult data based on the proportion of feather mass grown, for 11 weaver species, three of which are newly reported on. Timing of primary moult is discussed in relation to sex, location and annual timing. The duration of primary moult varies widely between and within species, from 46 days (1.5 months) in a widowbird to 215 days (7 months) in an arid species. Weavers in arid regions have longer moult durations than weavers in other regions. Examples of the overlap of primary moult and breeding are presented.

Time available for moulting shapes inter- and intra-specific variability in post-juvenile moult extent in wheatears (genus Oenanthe)

Moult is a vital and endogenously controlled process in the avian life. However, birds may modulate their feather renovation properties, such as the extent of moult, based on exogenous factors. Despite the large body of knowledge about moult patterns, numerous questions remain unclear. In this study, we aimed to improve our knowledge about the factors that affect variation in the extent of the post-juvenile moult in passerines by performing inter- and intra-specific comparative analyses. We assessed the effect of internal and external factors on passerines’ moult by comparing post-juvenile moult extent among 16 wheatear species (genus Oenanthe) from the Palearctic Ecozone. The tested factors included migration distance used as a proxy of time available for moulting and habitat type. We also explored the relationship between the extent of the moult, migration distance, and sex in the Northern Wheatear Oenanthe oenanthe across a latitudinal gradient in Western Europe. The results indicate that post-juvenile moult extent in wheatears was negatively related to migration distance, such that species with shorter migration distances moult extensively compared to long-distance migratory species. In contrast, the extent of post-juvenile moult in the Oenanthe genus was not related to preferred habitat type (arid or non-arid) of the species. Migration distance was also related to post-juvenile moult extent in the Northern Wheatear, with fewer renewed feathers in northern populations. However, the extent of the post-juvenile moult did not differ between sexes. Thus, our results support that time constraints affect moult extent in long-distance migratory species and populations.

Post-juvenile moult in Graceful Prinia Prinia gracilis

The moult pattern of the Graceful Prinia Prinia gracilis, a resident cisticolid warbler of the Middle East region of the Western Palaearctic, is poorly known. Characterising moult strategies in the avian life cycle is important for understanding population processes and dynamics and, therefore, we have analysed the timing, sequence, extent and duration of post-juvenile moult of Graceful Prinia in Israel. The extent of post-juvenile moult was either complete or partial (but extensive), depending on the dates of hatching and the start of moult. Compared to most European passerines, the long breeding period (February–November) in this region allows a relatively long moult period (79.3 ± 4.7 days) for this resident species, which facilitates considerable variability in the extent of post-juvenile moult.

Extent and symmetry of post-juvenile moult as predictors of future performance in Greenfinch Carduelis chloris

The extent of post-juvenile moult in passerines is highly variable, but the causes and consequences of such variability remain poorly understood. We tested the hypothesis that the extent and symmetry of post-juvenile moult of Greenfinches Carduelis chloris may be used as reliable predictors of their winter/spring body condition. We found a quadratic relationship between moult extent and the body mass/wing length ratio during the winter/spring period. We also found that Greenfinches with higher degree of moult symmetry had greater winter/spring fat reserves. Our results suggest that the extent and symmetry of post-juvenile moult may be considered as adaptive traits with certain fitness consequences.

Dependence of Postjuvenile Moult on Hatching Date, Condition and Sex in the Great Tit

We examined the influence of hatching date, nestling condition (body mass), size and sex on the age at the onset, and on the duration and extent of postjuvenile moult in a Great Tit population in southern Finland. Date of hatching explained most of the variation in moult parameters. Onset of moult was closely connected with hatching date: Great Tits from first broods started moulting in July and birds from second broods started in mid-August. The age at the start of moult decreased from 56 to 42 days from first to repeat and second broods and the duration of moult decreased from 67 to 59 days. Variation of moult parameters with date of hatching and the timing of moult are in concordance with experimental data on photoperiodic control of moult. Females started to moult older and moulted less extensively than males, especially in first broods. Residual body mass during moult reflected the state and intensity of moult, but did not correlate with the final extent of moult. This contradicts the recent protein stress and condition hypotheses.

Behavioural and morphological correlates of variation in the extent of postjuvenile moult in the SiskinCarduelis spinus

Siskins Carduelis spinus show great variation in the acquisition of adult plumage, so that yearling birds can be classified as either “delayed” (i.e. still showing yearling plumage) or “advanced” (i.e. with an adult plumaged appearance). The extent of moult in males is related to the size of their black bib, which in turn is highly correlated with their social dominance rank. Autumn male body mass is higher in advanced than in delayed moult birds, but by winter the relationship is reversed, suggesting a trade‐off between investment in moult and subsequent body condition. Results were similar in Spain and Britain. A possible cost of advancing moult is suggested by an analysis of aggressive interactions at bird feeding tables which showed that adult males discriminate between delayed and advanced birds, directing most aggression towards adult‐looking yearling males. The results suggest that the variation in the extent of postjuvenile moult is not only related to energetic constraints but has other important behavioural and ecological implications.

The timing of post-juvenile moult and fuel deposition in relation to the onset of autumn migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers Acrocephalus schoenobaenus

The extent of post-juvenile moult and fuel deposition prior to migration in Reed Warblers Acrocephalus scirpaceus and Sedge Warblers A. schoenobaenus were analysed using 11 years ringing data from Lake Kvismaren in South Central Sweden. Re-trap data showed that Reed Warblers acquired their first winter plumage in 34 days, compared to 22 days in Sedge Warblers. The moult pattern of the two species differed due to Sedge Warblers only undertaking a fill-in moult of bare body areas. Fuel deposition rates for the two species were similar, 0.38 g/day for Reed Warblers and 0.34 g/day for Sedge Warblers. The estimated average fuel stores at departure from Lake Kvismaren differed, with Reed Warblers found to leave with a fuel store of 21% (in relation to lean body mass) compared to 6.2% in Sedge Warblers. The median date of departure from Lake Kvismaren was estimated to 30 August for Reed Warblers and 12 August for Sedge Warblers. The earlier departure of Sedge Warblers, with smaller fuel stores, may reflect different migration strategies between the species.

Postjuvenile moult, phenology and biometry of Grey WagtailsMotacilla cinereamigrating over central Belgium

Active migration of Grey Wagtails was studied intensively during three autumns (1980, 1982, 1984) and partly during 1985 at an inland site in central Belgium. The total number of migrants observed was 720, and 416 birds were trapped. The most important passage was found during September and peaks occurred in the last fortnight of September and the first week of October. There was hardly any seasonal shift between years. This, together with the small overall shift in timing of passage over the whole range of distribution in western Europe points towards long‐distance migratory behaviour. The extent of postjuvenile moult is described for greater‐coverts, rectrices, tertials, alula‐feathers and the carpal covert. Eighteen juveniles were trapped on migration when still obviously growing new body‐feathers. There was a sharp decline in the mean extent of renewal of greater‐coverts, rectrices and tertials for all successive sub‐samples in the course of the autumn, which is mainly due to a gradual influx of birds with little additional postjuvenile moult. These were probably of mainly northern origin. There is generally little variation in Grey Wagtail measurements.